The thermometallurgical processes, such as especially the thermoalumino process and the thermosilico process for reduction of metal oxides to metals, have been known for a long time. Thus, for example, chromium metal and alloys such as ferrovanadium (FeV) and ferroniobium (FeNb), are produced aluminothermally and ferromolybdenum (FeMo) is produced silicothermally. Ferrotungsten (FeW) is produced alumino-silicothermally.
Such processes run generally discontinuously and a mixture prepared of metal oxide, reducing agent (Al,Si) and possibly even metals (Fe) is formed in a fixed or transportable reaction vessel and ignited. For this purpose one generally uses chemical or electrical starters.
Once ignition is initiated, the desired reaction occurs vehemently and at high velocity; inclusions are practically impossible since the reaction vessel can be closed with an evacuation hood which carries the hot waste gases to a gas-cleaning station.
After 2 to 4 minutes the metal phase separates from the slag phase and one can permit the contents of the reaction vessel to cool and solidify. Only limited conversions or yields can be obtained by these techniques.